In a wireless communications network, devices intend to communicate with other devices via a communications channel, at the highest possible rate, with the least possible transmitted power and at the lowest possible cost. The cost of a device is usually dictated by its complexity, while the communication rate between any two devices is limited by Shannon Channel capacity as defined by the communication medium between the two devices and by the corresponding transmitted power. Shannon Channel capacity is a theoretical limit on the communication rate, and does not offer an indication on the complexity of the device.
One way to increase Shannon Channel capacity between two devices is to adopt multiple antennas for each device. In the presently disclosed systems, antennas, which belong to one device, are allowed to cooperate. Another way to increase Shannon Channel capacity is to allow a group of devices to transmit simultaneously, to another group of devices. In the presently disclosed systems and methods, when a group of devices, such as a transmitting group or a receiving group, is able to cooperate, we refer to it as a cooperative group, otherwise, it is a non-cooperative group. For example, in a cellular network, a group of access nodes (e.g., LTE Base Stations) is often a cooperative group, however, a group of users (subscriber stations, handsets, nodes) is seldom a cooperative group.
In this description, we refer to the communication channel from a group of access nodes to a group of users as a Downlink (DL) Multi-User (MU) channel, while the communication channel from a group of users to a group of access nodes is referred to as an Uplink (UL) Multi-User (MU) channel. When a device has multiple antennas, we refer to it as a Multiple Input Multiple Output (MIMO) device. When a group of access nodes with multiple antennas transmit to a group of receiving users also with multiple antennas, the network is referred to as a DL MU-MIMO network. On the other hand, when a group of users with multiple antennas transmit to a group of receiving access nodes also with multiple antennas, the network is referred to as a UL MU-MIMO network.